Products, Vendors, CAD Files, Spec Sheets and More...
Sign up for LAWeekly newsletter
Maintaining municipalities, no matter how large or small, comes with the added challenge of planting trees in areas that are surrounded by concrete and unfriendly soil. With these additional constraints, effectively planting and growing trees in urban areas is always difficult.
To that end, a new method to help with these problems has hit the market that improves root growth in these situations, and at LSMP, while we do not endorse one product over another, we thought this was a new and unique tool that would be useful to Landscape Superintendents.
Through your varied experience, you understand that a city environment is especially tough for trees. Exaggerated heat and wind, generally poor soils only a few inches deep with limited drainage, plus pollution, shading, and other factors make it especially challenging.
Trees in general do poorly in city planting spaces for two basic reasons: failure of nurseries to develop tree root systems better suited to these conditions and insufficient space/ soil volume for root growth to sustain the tree following initial establishment.
Persistent poor performance of conventionally grown trees in city spaces forced researchers to investigate new approaches. Through their testing they have found a way to grow trees in such a way that success is more likely immediately following planting, in all but the most deplorable locations.
Further, they found that if trees are provided additional space, the appearance and functional lifetime could be increased substantially. Planting trees in spaces with less than 30 square feet of exposed soil surface typically provides only a brief glimpse of green in the plant top. Even for the toughest species this is then normally followed by a slow decline leading eventually to death.
Because of this fact superintendents prefer to plant one tree with a shallow, fibrous root system with at least 50 square feet or more of real estate, rather than planting three or four trees with inadequate space.
Trees grown conventionally in field nurseries typically have no roots in the top four to eight inches of the soil ball at time of planting into the landscape. This is due to a combination of deep planting initially of bare root stock and soil moved up and around the stem during cultivation. Bare root liners typically have a very poorly branched root system to begin with. To establish the tree, production of new roots out into the surrounding soil must occur.
With recently harvested balled-in-burlap plants, new root buds must first be initiated at the cut face of old roots. But this is a very oxygen-dependent process. It is only after initiation that root extension begins in whatever direction the old roots were oriented.
Once initiated, roots are typical of the species in general and more tolerant of poor aeration. A classic example is that of bald cypress, Taxodium distichum, which will grow in swamps. But, plant a bald cypress that was dug balled in burlapin an area where soils stay wet and oxygen is limiting and the tree will die. It is only after establishment and acclimation to the site that bald cypress will tolerate flooding.
The least desirable situation results from trees harvested balled-in-burlap and held above ground surrounded by mulch. Many roots are typically produced at the cut face of old roots because the mulch is well aerated. However, roots produced at the cut face of old roots consume energy but extend out into mulch material containing few nutrients. Further, these roots are mostly or entirely lost during transplanting. Following planting, new roots must again be initiated only under less favorable conditions of aeration and with fewer energy reserves in root tissues.
Limited space for root growth in city landscapes functions similar to growing plants in containers. With experience and experimentation it has become clear that a tree will grow and remain healthy in a given volume of container growth medium for a limited period of time. With smooth walled conventional containers, roots become concentrated and congested against the inner sidewall with little root exploration of the central volume of the container.
Once that volume is exploited, root exploration and nutrient mining is restricted and the tree begins to stagnate and decline. On the other hand, health and vigor can be retained far longer when a tree starts out with a fibrous root system and roots are stimulated to branch and never allowed to circle and become congested. This allows roots to fully utilize the limited volume available.
In order to grow trees best suited to city spaces air-pruning of the taproot must occur with a few days following seed germination. When air-pruning occurs about four inches below the seed, secondary and more horizontal roots form along the vertical axis of the very short, young, taproot. The key is to maintain roots mostly in a horizontal position with continued branching.
This is not an abnormal situation. In nature, mature trees end up with the bulk of their roots horizontal and in the upper 8 to 12 inches of soil. However, this occurs over a period of many years and after dominance by the taproot has been lost.
When catalpa trees were grown in identical white containers but one was lined with smooth plastic while the other had the capacity to trap root tips and stimulate root branching, root development was very different following transplanting. Having roots poised to grow horizontally from most of the vertical side of the root ball has distinct advantages but especially in restricted growing spaces.
Roots grow where conditions are favorable. If aeration is poor and roots can only function in the upper four to six inches of soil in a city planting site, that may be enough to sustain the plant until drainage progresses and allows root growth to a greater depth.
Trees grown with fibrous root systems and active white root tips at time of planting have a much greater likelihood of success in restricted city spaces.
The fibrous root system can immediately begin to exploit any favorable soil volume that exists. However, a fact of life is that at some point, volume of soil suitable for root exploration becomes the limiting factor and tree decline begins just as occurs in a container. However, trees grown with fibrous shallow root systems have the capacity to function well in restricted city spaces much longer than conventional field grown trees.
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
Sign up to receive Landscape Architect and Specifier News Magazine, LA Weekly and More...
Invalid Verification Code
Please enter the Verification Code below
You are now subcribed to LASN. You can also search and download CAD files and spec sheets from LADetails.